﻿<%@ WebHandler Language="C#" Class="Captcha" %>

using System;
using System.Web;
using System.Drawing;
using System.IO;
using System.Web.SessionState;

public class Captcha : IHttpHandler, IRequiresSessionState{
    
    public void ProcessRequest (HttpContext context) {
        int codelength = Int32.Parse( context.Request["codelength"]);
        string validateNum = CreateRandomNum(codelength);
        using (MemoryStream ms = CreateImage(validateNum))
        {
            context.Session["LoginCaptcha"] = validateNum;
            context.Response.ContentType = "image/Gif";
            context.Response.BinaryWrite(ms.ToArray());
            context.Response.End();
        }
    }
    //生产随机数
    private string CreateRandomNum(int NumCount)
    {
        string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
        string[] allCharArray = allChar.Split(',');//拆分成数组
        string randomNum = "";
        int temp = -1;                             //记录上次随机数的数值，尽量避免产生几个相同的随机数
        Random rand = new Random();
        for (int i = 0; i < NumCount; i++)
        {
            if (temp != -1)
            {
                rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
            }
            int t = rand.Next(35);
            if (temp == t)
            {
                return CreateRandomNum(NumCount);
            }
            temp = t;
            randomNum += allCharArray[t];
        }
        return randomNum;
    }
    //生产图片
    private MemoryStream CreateImage(string validateNum)
    {
        MemoryStream ms;
        //if (validateNum == null || validateNum.Trim() == string.Empty)
        //    return null;
        //生成BitMap图像
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(validateNum.Length * 12 + 12, 22);
        Graphics g = Graphics.FromImage(image);
        try
        {
            //生成随机生成器
            Random random = new Random();
            //清空图片背景
            g.Clear(Color.White);
            //画图片的背景噪音线
            for (int i = 0; i < 25; i++)
            {
                int x1 = random.Next(image.Width);
                int x2 = random.Next(image.Width);
                int y1 = random.Next(image.Height);
                int y2 = random.Next(image.Height);
                g.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2);
            }
            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
            g.DrawString(validateNum, font, brush, 2, 2);
            //画图片的前景噪音点
            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(image.Width);
                int y = random.Next(image.Height);
                image.SetPixel(x, y, Color.FromArgb(random.Next()));

            }
            //画图片的边框线
            g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
            ms = new MemoryStream();
            //将图像保存到指定流
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
        return ms;
    } 
    public bool IsReusable {
        get {
            return false;
        }
    }

}